Share date, voice, tone, spelling, and hardware behavior

Provide common date/time formatting, locale voice matching, tone synthesis, phonetic spelling, and one hardware synthesizer protocol encoder for both readers. Standardize whiskey and x ray and use the tested Fenrir DECtalk mapping.

Validated the common module with GOWORK=off go test -race ./...; reader integration, serial cancellation, PCM hashes, no-CGO datetime, and speech regression checks passed. Physical keyboard, audible synthesis, and braille acceptance remain separate live checks.

phonetic/phonetic.go

@@ -0,0 +1,18 @@
+// Copyright (c) 2026 Storm Dragon
+// Authors: Storm Dragon, Angus Kola
+// SPDX-License-Identifier: GPL-3.0-or-later
+
+// Package phonetic supplies the common spelling alphabet.
+package phonetic
+
+import "unicode"
+
+// Letter returns a lowercase spelling word, or empty for non-Latin letters.
+func Letter(char rune) string {
+	words := [...]string{"alpha", "bravo", "charlie", "delta", "echo", "foxtrot", "golf", "hotel", "india", "juliet", "kilo", "lima", "mike", "november", "oscar", "papa", "quebec", "romeo", "sierra", "tango", "uniform", "victor", "whiskey", "x ray", "yankee", "zulu"}
+	char = unicode.ToLower(char)
+	if char < 'a' || char > 'z' {
+		return ""
+	}
+	return words[char-'a']
+}

phonetic/phonetic_test.go

@@ -0,0 +1,16 @@
+// Copyright (c) 2026 Storm Dragon
+// SPDX-License-Identifier: GPL-3.0-or-later
+package phonetic
+
+import "testing"
+
+func TestSharedSpellingAndFallback(t *testing.T) {
+	for _, row := range []struct {
+		char rune
+		want string
+	}{{'a', "alpha"}, {'A', "alpha"}, {'w', "whiskey"}, {'W', "whiskey"}, {'x', "x ray"}, {'X', "x ray"}, {'É', ""}, {'界', ""}, {'1', ""}} {
+		if got := Letter(row.char); got != row.want {
+			t.Fatal(row, got)
+		}
+	}
+}